The invention relates to apparatus for pressurizing the rear suspension of a vehicle provided with air springs, when one end of a container or similar is lifted onto the rear-end of the vehicle by a load handling system of the hook-lift type.
There are many known designs of vehicles with load handling systems of a variety of different hook-lift types. In one known arrangement, a commercial vehicle has a load handling system which is arranged to load and unload over the rear end of the vehicle chassis. The most demanding phase of the loading operation arises during the first part of the loading when the front end of a container, a flatrack or a similar load carrier is being lifted up over the rear end of the vehicle to make initial contact with the rollers or similar guide means which will support and guide the container during the rest of the loading movement.
During the initial phase of the loading, the air springs of at least the rearmost axle may be compressed to the extent that they reach the load limit and contacts their bump stops. This can be caused by the driver starting the loading before the air springs in the suspension have had time to build up a sufficient pressure to support the sudden increase in load. This is a particular problem if the vehicle is unloaded, in which case both the pressure in the air springs and the spring stiffness are relatively low. In this case, the filling of the air springs will not begin until a signal is transmitted from sensors monitoring a change in height of the vehicle chassis. This process will usually be too slow to allow the air springs to be pressurized to take the load.
Also, unknown to the driver, the container itself may be too heavy for the vehicle suspension. If an insufficiently pressurized suspension is subjected to an overload condition, this may cause buckling of parts of the air springs and even deformation of the rear end of the vehicle chassis.
One solution to this problem is to provide the vehicle with support legs that may be deployed by hydraulic cylinders. Support leg of this type will take the load but requires a separate hydraulic system, which adds to the weight, complexity and cost of the vehicle. A further problem with such legs is that the loading of the vehicle will be more time consuming, as the driver must first ensure that the ground below the vehicle is stable, then deploy the legs, and finally retract them after a completed loading operation.
It is desirable to provide an improved arrangement for pressurizing the rear air springs of a vehicle during operation of a load handling system of the hook-lift type, which arrangement assists the driver in avoiding the above problems.
In the text below, the term “air spring” is intended to encompass all types of pneumatic springs comprising a resilient, elastic or similar member used in a vehicle suspension. The axle to be lifted is preferably a so-called trailing axle that is not driven. However, the invention may be adapted to other types of axles in a commercial vehicle.
In addition, air springs are connected to a source of compressed air via one or more controllable valves, whereby the air springs may be pressurized or vented by means of said valves. However, the means for controlling the pneumatic pressure in the air spring or any valves for controlling auxiliary devices will not be described in detail. As these components are not part of the inventive idea, they will only be discussed briefly in the text and shown schematically in the drawings.
The An aspect of the invention relates to an arrangement for a vehicle suspension comprising air springs, which vehicle comprises at least one front axle and at least two rear axles. In the text below, aspects of the invention is are mainly described in relation to a vehicle having a load handling system of the hook-lift type, where the invention is intended for assisting pressurization of said air springs during loading of a freight container onto a rear end of the vehicle by the load handling system. However, aspects of the invention may also be applied to other type of load handling vehicles, such as dump trucks, wherein the suspension may be subjected to a sudden increase in load that in some cases may cause damage to the vehicle and/or the vehicle suspension.
Commercial or construction vehicles suitable for application of aspects of the invention are provided with means for lifting at least one of the rear axles of the vehicle. The vehicle may have a plurality of rear axles having axle members which are in the form of cross-members and support the chassis of the vehicle by way of corresponding pairs of pneumatic suspension air springs supplied from a compressed air source. The vehicle may comprise a lifting assembly located in each, adjacent both or in between a corresponding pair of air springs on the axle to be lifted. The lifting assembly is at least one air spring expansible by the effect of the pressure of the compressed air source, such as a compressor or an accumulator and suitable valves to maintain said axle in the raised position when its suspension air springs are load-free.
An aspect of the invention relates to an arrangement for a suspension for a load carrying vehicle, which suspension is provided with air springs and comprises at least one front axle and at least two rear axles, and where each rear axle is provided with at least one pair of corresponding suspension air springs and at least one air spring is provided for lifting one of said rear axles.
The suspension air springs for at least the rearmost axle is connected to the air spring for lifting one of said rear axles by a conduit for compressed air, which conduit is provided with a controllable valve, whereby the controllable valve is arranged to open during a vehicle loading process.
For a vehicle with two rear axles, the axle to be lifted is a non-driven axle and may be either the forward or the rearward axle. The invention can also by applied to vehicles with three rear axles, wherein at least one non-driven axle may be lifted. At least one air spring may be used for lifting each of said non-driven rear axles. As stated above, the suspension air springs of at least the rearmost axle is connected to the lifting air spring. If two separate air springs are used for lifting an axle, each lifting air spring may be connected to a separate suspension air spring via separate, but simultaneously actuated controllable valves. Similarly, for a vehicle with three rear axles with a single driving axle, two separate air springs may be used for lifting one axle each. Each lifting air spring may be connected to the suspension air springs of separate axles via separate, but simultaneously actuated controllable valves.
The lifting air spring may be arranged to be pressurized prior to the vehicle loading process. For a vehicle with a hook-lift load handling system, pressurizing of the lifting air spring can be actuated by the driver as the vehicle is being maneuvered into position for loading a container or similar. The suspension air springs for the axle to be lifted by said lifting air spring is arranged to be pressurized to balance the pressure in the lifting air spring, in order to prevent said axle from being lifted. For instance, if the a lifting air spring is pressurized to the supply pressure of the pneumatic system of the vehicle, for instance 12 bar, the suspension air spring may be pressurized to at least maintain ground contact, for instance 2 bar. These pressures may vary depending on the type and the size of the vehicle, the available supply pressure from a compressor or an accumulator, the relative size of the lifting and suspension air springs, and other parameters.
If the vehicle travels unloaded, with a non-driven axle in a lifted position, then the lifting cylinder is already pressurized to the supply pressure of the pneumatic system. Actuation of the arrangement by the driver will then cause the suspension air spring to be pressurized to lower the lifted axle in order to at least achieve ground contact.
When the above-mentioned controllable valve is opened during a vehicle loading process, the pressurized air in the one or more lifting air springs will be supplied to the suspension air springs of at least the rearmost axle through said conduit. This equalization of pressure between the lifting and suspension air springs causes a relatively rapid increase of the pressure in the suspension air springs. In this way, the rear suspension of the vehicle may support a sudden increase in load during an initial period of a loading process, until additional pressure can be provided by the compressed air supply of the vehicle.
According to a further aspect, the suspension air springs may comprise a pot made of rigid, pressure-resistant material, such as steel or a suitable plastic material, and a resilient bellows closed by a substantially flat plate at one end and at its opposite end fitted onto an open end of the pot, made of e.g. nylon-reinforced rubber. The bellows is in pneumatic connection with the pot and is connected to a source of compressed air via at least one controllable valve. An air spring of this type may be provided with a pot having an air shut-off valve in a partition wall arranged to shut off the open end facing the bellows, creating a separate pressure tight chamber inside the pot. The volume of this chamber may be as much as half of the total volume of the air spring.
The controllable valve may comprise a seat or poppet valve a sliding valve or a rotary valve, which valve may be controlled pneumatically or electrically.
In the case of a poppet valve, the poppet may be raised and lowered by means of a piston in a separate cylinder inside the pot, arranged to shut off the air inside the pot, in a lowered position, while air is being vented from or supplied to the bellows, and to equalize pressures between the pot and the bellows, in a raised position, when air is neither vented from or supplied to the bellows. The opening and closing of the poppet is controlled by a pressure supplied to the cylinder when it is desired to open the poppet valve.
In this aspect, the above arrangement may be used in combination with the air spring for lifting one of said rear axles. For instance, when a rear axle is to be lifted the pressure supplied to the poppet valve is shut off, causing the poppet valve to close and retain the current air pressure. This pressure may in some cases be as much as 8 bar. To lift the axle, the volume contained within the bellows is vented to the atmosphere as the lifting air spring is pressurized.
During a subsequent loading operation, as described above, the controllable valve between the one or more lifting air springs and the suspension air springs of at least the rearmost axle is opened and the pressurized air in the lifting air springs will be supplied to the suspension air springs through said conduit. This first equalization of pressure between the lifting and suspension air springs causes an initial increase of the pressure in the suspension air springs. Subsequently, pressurized air is supplied to the cylinder to open the poppet valve. This causes a further increase in pressure during a second equalization of pressure between the bellows and the pot. Depending on the pressure in the volume contained in the pot, it may be necessary to close the controllable valve between the suspension and lifting springs before the poppet valve is opened to maintain the pressure in the suspension air spring. Alternatively, a non-return valve may be provided in the conduit. This provides the rear suspension of the vehicle with additional pressure for supporting a sudden increase in load during an initial period of a loading process, until additional pressure can be provided by the compressed air supply of the vehicle.
According to a further aspect, the vehicle may be provided with a signal generating means, arranged to generate a signal when a vehicle loading process is in progress, whereby the signal is arranged to open said controllable valve. According to one aspect, the signal generating means may be a switch controllable by an operator. For instance, this may be the switch used to initialize the loading process, whereby a pneumatic or hydraulic means are moved to load the vehicle.
According to a further aspect, the signal generating means is a load sensor for indicating that the vehicle is subjected to a load exceeding a predetermined value. This may be a weight sensor or a strain gauge monitoring the current load applied to one or more positions of the vehicle or to a load carrying platform thereon.
According to a further alternative, the signal generating means is a sensor for indicating that the vehicle is subjected to a load causing a predetermined compression of at least the rear most suspension air spring. This may be a height sensor measuring the relative distance between a fixed position on the vehicle chassis and a suitable position on a vehicle axle. Sensors of this type are may be available on many types of commercial vehicles, whereby an existing signal output may be used.
An aspect of the invention further relates to a method for assisting pressurization of said air springs for loading of a freight container onto a rear end of the vehicle by the load handling system of the hook-lift type, which vehicle comprises at least two rear axles, each axle provided with at least one pair of corresponding suspension air springs for each rear axle and at least one air spring for lifting one of said rear axles. The method may involve the steps of; -pressurizing the air spring for lifting one of said rear axles prior to actuation of the load handling system,                pressurizing the suspension air springs of the axle to be lifted to prevent said lifting air spring from lifting said axle;        generating a signal indicating that a vehicle loading process is in progress;        actuating a valve for connecting the lifting air spring to the suspension air springs of at least the rearmost axle in response to the signal.        
According to a further aspect, generation of the signal may be achieved by a sensor indicating that the rear part of the vehicle is subjected to a load. According to a further aspect, generation of the signal may occur when the load handling system is actuated to load the vehicle. According to a further aspect, generation of said signal may occur when a sensor indicates that the vehicle is subjected to a load causing a predetermined compression of at least the rear most suspension air spring.
An aspect of the invention further relates to a vehicle provided with an arrangement according to one or more of the above embodiments.